There are a number of assays and sensors for the detection of the presence and/or concentration of specific substances in fluids and gases. Many of these rely on specific ligand/antiligand reactions as the mechanism of detection. That is, pairs of substances (i.e. the binding pairs or ligand/antiligands) are known to bind to each other, while binding little or not at all to other substances. This has been the focus of a number of techniques that utilize these binding pairs for the detection of the complexes. These generally are done by labelling one component of the complex in some way, so as to make the entire complex detectable, using, for example, radioisotopes, fluorescent and other optically active molecules, enzymes, etc.
Other assays rely on electronic signals for detection. Of particular interest are biosensors. At least two types of biosensors are known; enzyme-based or metabolic biosensors and binding or bioaffinity sensors. See for example U.S. Pat. Nos. 4,713,347; 5,192,507; 4,920,047; 3,873,267; and references disclosed therein. While some of these known sensors use alternating current (AC) techniques, these techniques are generally limited to the detection of differences in bulk (or dielectric) impedance.
The use of electrophoresis in microfluidic methods to facilitate the binding of biological molecules to their binding partners for subsequent detection is known; see for example U.S. Patent Nos. 5,605,662 and 5,632,957, and references disclosed therein.
Similarly, electronic detection of nucleic acids using electrodes is also known; see for example PCT US 97/20014 and U.S. Pat. No. 5,770,369.
However, there is a need for a system that combines electrophoretic transport of target analytes, including nucleic acids, to a detection electrode for subsequent electronic detection.